To interact properly and appropriately with the world around us, it is important for us to not only see what it around us, but also to understand it. This occurs through a process known as visual processing, where our brain tries to make sense of what we see with our eyes.

When we look at something, our brain not only takes note of the physical attributes of what we see, but it also tries to understand the meaning behind these physical attributes. For instance, when you look at a television set, you don’t just see its shape, size and color; you also gain understanding about what it means.

You automatically understand that it requires electricity to operate, you know that you might need a remote controller to operate it, you know you can catch the news on it if you switch it on, and so on. All this happens automatically and unconsciously.

Without even thinking about it, your brain processes all this information when you simply look at an object.


In a bid to gain more understanding about how our brains process visual information, an American psychologist by the name John Ridley Stroop conducted an experiment that came to be known as the Stroop Test. The Stroop test itself is quite simple and involves two steps.

In the first step, a participant is presented with a list of words for colors. The words are printed in colored ink whose color is different from the color denoted by the word. For instance, the word “blue” might be printed in red ink.

The participant is then asked to read through the words as quickly as possible, without paying any attention to the color in which the word is printed. The participant is timed as they read through the words.

To illustrate the first step of the experiment, below is a group of words for colors whose color is different from the color denoted by the word. Time yourself and note how long it takes you to read through the words while ignoring the color in which they appear.


How did you fare? I bet you read through the words quite fast.

In the second step of the experiment, the participant is once again presented with a list of words for colors, with the words printed in in colored ink whose color is different from the color denoted by the word.

However, this time the challenge is a bit different. Instead of reading out the words, the participant is required to name the color in which the word is printed. For instance, if the word “brown” is printed in yellow ink, the participant should say “yellow” instead of brown. They should ignore what the word says and focus on its color.

Once again, below is a list of words for colors printed in colors that are different from the colors denoted by the words.

Time yourself as you go through the words, saying out loud the color in which they are printed while ignoring what the word says.


How did you fare this time round? Did it take you much longer to read through the words? Did you find it hard to actually name the color the words are printed in rather than what the word says? Below is a video of the test.

When J. R. Stroop conducted his experiments in 1935, he noticed that the participants had a harder time naming the color compared to simply reading out the words. He attributed this to a phenomenon that has come to be known as the Stroop effect, named after him.

The Stroop effect is the interference (mind flub) you just experienced when trying to name the colors while ignoring what the words say. Your brain was trying to process two conflicting mental processes, both of which were simultaneously competing for your brain’s attention and prominence.

The Stroop effect provides evidence that the embedded knowledge we have about our environment has an influence on how we interact with the environment. It also shows that we are not always in control of what our brains choose to pay attention to. But why does this interference occur?

The Stroop test reveals that our brains are automatically inclined to read any text we come across. As an adult, you have been reading words for so long that it becomes an effortless and automatic process that does not require any significant cognitive effort and that you cannot avoid.

Seeing a word and trying to avoid reading it is like trying to avoid thinking about an elephant when someone says “don’t think of an elephant.” You just can’t do it. In the experiment, you are trying to focus on the color the word is printed in, but your brain cannot avoid reading what the word says.

This gives you two bits of conflicting information (the actual color you see, and the color you think of after reading the word). To solve this conflict and come up with the required answer, your brain has to expend more cognitive effort.

Having to take in two conflicting bits of information and then resolve the difference between them slows down your response, which is why it takes you longer to go through the second set of words.

Out of practice (years upon years of reading) our word-recognition ability is much faster than our color recognition ability. This means that most people will recognize what a word means before they recognize the color in which it is written.

In addition, out of experience, our brains have learnt that the meaning of a word is more important than the color it is written in. So, in essence, our brains have learnt to ignore the color and focus on what the word says. However, the exercise requires you to name the color and not the meaning of the word.

Therefore, your brain has to inhibit the word recognition process, which is faster, in order for the color recognition process to provide the correct response. This inhibition requires something known as selective attention.

Sometimes, your brain, in its impulsivity, is unable to suppress the faster word recognition process, which is why you might have given a few erroneous answers, reading out the word instead of naming the color it is written in.

Because of this, the Stroop test is used to test for mental processes associated with conditions such as Attention Deficit Hyperactivity Disorder (ADHD). Subjects with ADHD are more likely to make more errors and to take longer in the second step of the Stroop test.

This is because the brains of people with ADHD are more prone to impulsivity and therefore have a harder time inhibiting the much faster word recognition process to allow the color recognition process to provide the correct response.

The inhibition of some mental process is facilitated by the neurotransmitter dopamine, which is why ADHD patients are usually treated by restoring their levels of dopamine, which in turn suppresses their impulsivity.

The Stroop effect happens automatically; there is not much we can do to prevent it. To show how automatically it happens, the Stroop effect is even said to have been used by American intelligence agents to catch a man suspected of being a Russian spy.

Apparently, the man, who claimed not to know Russian, was presented with the Stroop test, but with the words for colors written in Russian instead of English.

When asked to name the colors of the words, the man had a slow response rate when the words and colors were incongruent (the word was written in a color that was different from the color denoted by the word).

This was a signal to the American intelligence agents that the man could actually speak Russian, despite claiming otherwise.


There are a number of different theories that have been used to explain the Stroop effect.

While the theories differ in the part of visual processing that they emphasize, all the theories are unified by the central premise that it is much simpler and more automatic to read a word than to recognize and name a color, and that a conflict between the two processes will lead to increased cognitive effort and slower processing times.

These theories are also sometimes referred to as ‘race models’ because all have an underlying notion that both pieces of information (the meaning of the word and the color) are processed simultaneously, but then they ‘race’ to enter the central processor first when it comes to selecting a response.

Below are the different theories used to explain the Stroop effect:

Speed of Processing Theory

This theory proposes that the lag experienced when trying to name the color but not the word occurs the brain can recognize words faster than it can recognize colors. In other words, the theory proposes that word processing and color recognition occur at different speeds, with word processing occurring much faster.

Therefore, when one is required to state the color, the information about what the word actually says arrives at the decision making stage before information about the color in which the word is written.

However, since the information that arrives first is not relevant in this case, this leads to processing confusion. It becomes more difficult to name the color after we have already read the word.

In the first step of the experiment, where the participant is required to read out the word and ignore the color, there is no conflict because the relevant information (what the word says) arrives faster than the irrelevant information (color).

Selective Attention Theory

According to the Selective Attention Theory, color recognition requires more attention compared to simply reading a word.

This in turn means that color recognition takes longer, either as the brain allocates the extra attentive resources required or as it tries to inhibit distractions from sources of information that do not provide the appropriate response (word recognition).

Automaticity Theory

The Automaticity Theory is the one that is most commonly used to explain the Stroop effect. According to this theory, out of habitual reading, our brains have gotten to a point where reading occurs automatically. It does not require any focused attention.

When you look at a word, your brain automatically engages it and understands what the word means. Color recognition, on the other hand, is not an automatic process. It requires some focused attention.

Therefore, when you look at a word, your brain automatically recognizes what the word is saying while it takes a bit longer to process the color, leading to slower response times.

Parallel Distributed Processing Theory

According to the parallel distributed processing theory, as the brain analyzes and processes information, it develops different and specific pathways to process different tasks. The strength of the pathways depends on the frequency with which the pathways are used.

When two pathways are activated at the same time, information in the stronger pathway is processed before the information in the weaker pathway. Since you read a lot more frequently than you are required to identify the color words are written in, the reading pathway is a lot stronger than the color identification pathway.

During the Stroop effect, both pathways are activated simultaneously.

Since the reading pathway is stronger, this information is processed first. However, since the appropriate response requires information from the weaker pathway, this leads to interference and slower response times.


The Stroop test and the Stroop effect have a number of uses is psychology. The test is very useful in evaluating a person’s attentional capacity, their cognitive processing speed, their selective attention capacity and their level of executive function.

These facets give psychologists a glimpse into how we interact with the world us. In other words, the Stroop test helps give psychologists a more detailed understanding of human thought and behavior. It helps them to observe the cognitive processes that drive explicit thought and provides insights into how the non-conscious brain works.

The Stroop test is also used in conjunction with other neuropsychological assessments in the diagnosis of neurological and neurodevelopmental disorders such as autism and schizophrenia.

The interference resulting from the Stroop Test has also been found to be more pronounced in people suffering from conditions such as ADHD, dementia, brain damage, and addictions to drugs, alcohol and gambling.

In addition, researchers also use the Stroop test in conjunction with brain imaging studies to understand the regions of the brain that are involved in processes such as decision making, planning and managing interference in the real world, such as talking on a phone while driving or studying for an exam when the television is on.

People have also recently started using variations of the Stroop test as exercise to help them improve their directed-attention skills and increase their mental vitality. The test can also be used as an exercise to help people hone their ability to control impulsive behavior.

During a Stroop test, the participant is required to overcome the impulse to respond to the initial and stronger stimuli and instead focus on a weaker stimuli. The better you become at inhibiting the urge to read instead of reporting the color, the better your brain will become at controlling impulsive behavior.


Aside from the original Stroop test, there have been other variations of the test which evaluate the effect of other sensory variables on interference. Below are some of the most popular variations of the test.

Warped Words Stroop Test

This variation is quite similar to the original Stroop test, with words for colors printed in ink color that is different from the color denoted by the word. However, this test takes things a step further. The words are also warped (curvy shaped). The aim here is to make the words more difficult to read.

The idea behind this test is that making the words harder to read slows down the brain’s reaction and processing time.

Surprisingly, the findings from the warped words Stroop test are similar to those from the original test. Participants still take longer to identify the color compared to reading the words.

Emotional Stroop Test

The emotional Stroop test gives psychologists a glimpse into how the brain processes information related to emotions. In the emotional Stroop test, negative emotional words, such as “sadness,” “sorrow,” and “depression” are placed in between neutral words such as “car,” “television,” and “house”.

The words are printed in different colored ink, and just like in the original Stroop test, the participant is supposed to name the color each word is written in, while ignoring what the word says.

According to researchers, participants suffering from depression will take longer to name the colors on negative emotional words compared to the colors of neutral words. In the emotional Stroop test, the interference arises from the conflict between the color of the word and the emotional relevance of the word to the participant.

Animal Stroop Test

This is a variation of the Stroop test that is used with young children. Normally, the Stroop effect occurs in adults because they have been reading for years, to the extent where reading comes automatically to them. However, for young children, reading is not very well established or fluent, and therefore does not come automatically.

Children below the age of 6 can barely even read the words, therefore there would be no conflicting information to allow psychologists to measure interference. Provided the children know their colors, they would perform relatively well in the Stroop test because the words do not mean anything to them.

In order for young children to effectively undertake the Stroop test, the test needs something the children can do automatically. This is where the animal Stroop test comes in. By the age of 4, most children can name common animals when presented with the pictures of the animals.

In fact, when presented with these pictures, most young children will name the animals without being prompted. In other words, it comes to them automatically.

In the animal Stroop test, the children are presented with pictures of animals, with a small twist. The heads of the animals have been swapped. For instance, the head of a cow might be placed on a dog, while the head of a dog is placed on a duck. The children are then asked to name the animal based on its body instead of its head.

Since the head of the animal is more prominent, the children are automatically drawn to it. In order for them to provide the correct response, they have to inhibit the automatic response (naming based on the head) and name the animal based on its body.

Studies conducted using the animal Stroop test find that children experience the same kind of interference that adults experience with the original Stroop test.

Spatial Stroop Test

This is a variation of the Stroop test that is used to investigate the interference between an objects location and the location information derived from the object. In this test, an upward or downward-facing arrow appears randomly above or below a line.

The participant is required to report the direction of the arrow (whether it is pointing up and down) while ignoring the arrows location relative to the line.

Researchers found that responses are faster and more accurate when the stimuli is congruent (for instance, an upward facing arrow appearing above the line) compared to when the stimuli is incongruent (for instance, an upward facing arrow appearing below the line).


The Stroop test has become a popular and widely used methodology that allows psychologists and researchers to get a peek into our brain functions and our implicit cognitive functions.

The Stroop effect occurs when our minds are required to inhibit the response from an automatic stimuli and give more relevance to the response from a weaker stimuli.

The test examines our ability to suppress our impulses and direct our attention where we want it at a particular time. The Stroop test is a simple exercise that you can do from anywhere. Give it a try and tell us how you fared in the comments below.

The Stroop Effect: Naming the Color but Not the Word

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